Corn (Zea Mays L.) silage in the northeastern USA yields more in narrow (0.38 m) vs. conventional (0.76 m) rows. Dairy producers, however, have considered converting from conventional to twin rows (0.19 m on 0.76 m centers) because twin are more compatible than narrow rows for herbicide application on glyphosate-resistant corn. Two hybrids were planted in field-scale studies in New York in 2003 and 2004 to evaluate growth, yield, quality, and economics of corn silage under conventional, narrow, and twin rows. Narrow rows had greater dry matter yield (17.6 Mg ha-1) than twin (17.2 Mg ha-1) and conventional rows (16.6 Mg ha-1). Row spacing did not affect in vitro true digestibility. Narrow and twin rows had greater fixed and variable costs, associated with equipment requirements. Partial budget analyses, however, indicated greater expected increases in annual profit with the conversion from conventional to narrow rows for 262 ($18201) and 525 ha ($38317) or to twin rows for 262 ($8246) and 525 ha ($17584) of corn silage. Although narrow vs. twin rows had more profit, use of glyphosate-resistant corn in twin rows may delay herbicide application until mid-June increasing the probability of a timely first harvest of perennial forages. Dry matter content at harvest, however, averaged 326 in narrow vs. 314 g kg-1 in twin rows increasing the probability of corn silage harvest before a fall frost. Dairy producers should consider economics as well as timely harvests when considering corn silage row spacing systems.